Yes I have JecsTools installed and loaded before cosmic horrors.

I am having a similar problem

Do you also get animals 'fleeing' across the map spewing blood despite having no injuries?

I do, I thought it was the mobs themselves until i turned on the dev log.

Exception ticking ROM_DarkYoung326136: System.TypeLoadException: Could not load type 'JecsTools.GrappleUtility' from assembly 'CosmicHorror'.
at (wrapper dynamic-method) Verse.Thing.TakeDamage_Patch1 (object,Verse.DamageInfo) <0x00276>
at RimWorld.Verb_MeleeAttack.ApplyMeleeDamageToTarget (Verse.LocalTargetInfo) <0x000ee>
at RimWorld.Verb_MeleeAttackBase.TryCastShot () <0x003e0>
at Verse.Verb.TryCastNextBurstShot () <0x00040>
at Verse.Verb.VerbTick () <0x0005c>
at Verse.VerbTracker.VerbsTick () <0x00034>
at Verse.Pawn.Tick () <0x00117>
at CosmicHorror.CosmicHorrorPawn.Tick () <0x00013>
at Verse.TickList.Tick () <0x002c6>

Verse.Log:Error(String)
Verse.TickList:Tick()
Verse.TickManager:DoSingleTick()
Verse.TickManager:TickManagerUpdate()
Verse.Game:UpdatePlay()
Verse.Root_Play:Update()

I have a dark young issue too:

ROM_DarkYoung892278 meleed Alpaca922404 from out of melee position.
Verse.Log:Warning(String)
RimWorld.Verb_MeleeAttackBase:TryCastShot()
Verse.Verb:TryCastNextBurstShot()
Verse.Verb:VerbTick()
Verse.VerbTracker:VerbsTick()
Verse.Pawn:Tick()
CosmicHorror.CosmicHorrorPawn:Tick()
Verse.TickList:Tick()
Verse.TickManager:DoSingleTick()
Verse.Game:<LoadGame>m__3()
Verse.LongEventHandler:ExecuteToExecuteWhenFinished()
Verse.LongEventHandler:UpdateCurrentAsynchronousEvent()
Verse.LongEventHandler:LongEventsUpdate(Boolean&)
Verse.Root:Update_Patch1(Object)
Verse.Root_Play:Update()

Could an alternate version of the mod be made, one that doesn't have the buggy Dark Young?

nothing spawning on my end it just been crashing the game?
Last update for rimworld deleeted alot of major code for cosmic horror DX

In the present day I'd say I'm coping just fine with 4 tame Dark Young, so long as you pretend the insanity loss all of my colonists are suffering from isn't there. Who needs wildlife when you can just go insane instead of eating?
..Anyhow, the point's that the thread is redundant now, if it ever wasn't before. Just felt like clarifying that for anyone who hadn't used the mod wondered whether it was stable..